Human cardiotrophin-1: protein and gene structure, biological and binding activities, and chromosomal localization

Cardiotrophin-1 (CT-1): a novel hypertrophic and cardioprotective agent

Cardiotrophin-1 (CT-1) is a member of the IL-6 family of cytokines which was originally discovered as a factor which can induce hypertrophy of cardiac myocytes both in vitro and in vivo. Subsequently, CT-1 has been shown to have a wide variety of different effects on cardiac and non cardiac cells including the ability to stimulate the survival of both cardiac and neuronal cells. Interestingly, whilst activation of the p42/p44 MAP kinase pathway is necessary for the survival promoting effects of CT-1 in cardiac cells, it is not required for its hypertrophic effect which is likely to involve activation of the Jak/STAT-3 pathway. CT-1 may therefore be of use as a novel cardio-protective agent, particularly if its hypertrophic effect can be specifically inhibited.

Cloning and characterization of the 5'-flanking region of the human cardiotrophin-1 gene

To enable the analysis of the regulation of the human cardiotrophin-1 gene expression, the 5'-flanking region of the human cardiotrophin-1 gene was cloned and sequenced. Data bank search revealed several cis- active DNA elements (SP1, CREB, C/EBP, AP1 and AP-2 like and GATA) in the proximal 1.1 kb region. Six nested 5-'terminal deletion mutants from -1091/+39 to -218/+39 were fused to a luciferase reportergene and proved to be functionally active after transfection into COS-7 cells.

Signaling of the cardiotrophin-1 receptor. Evidence for a third receptor component

Cardiotrophin-1 (CT-1) is a recently isolated cytokine belonging to the interleukin-6 cytokine family. In the present study we show that CT-1 activates its receptor expressed at the surface of a human neural cell line by recruiting gp130 and gp190/leukemia inhibitory factor receptor beta, as shown by analyzing their tyrosine phosphorylation level. Neutralizing antibody directed against gp130 and reconstitution experiments performed in the COS-7 cell line demonstrate that gp130-gp190 heterocomplex formation is essential for CT-1 signaling. Analysis of the subsequent activation events revealed that CT-1 induces and utilizes Jak1-, Jak2-, and Tyk2-associated tyrosine kinases, which are in turn relayed by STAT-3 transcription factor. Cross-linking of iodinated CT-1 to the cell surface led to the identification of a third alpha component in addition to gp130 and gp190, with an apparent molecular mass of 80 kDa. Removal of N-linked carbohydrates from the protein backbone of the alpha component resulted in a protein of 45 kDa. Our results provide evidence that the CT-1 receptor is composed of a tripartite complex, a situation similar to the high affinity receptor for ciliary neurotrophic factor.

Cardiotrophin-1, a cytokine present in embryonic muscle, supports long-term survival of spinal motoneurons

The muscle-derived factors required for survival of embryonic motoneurons are not clearly identified. Cardiotrophin-1 (CT-1), a cytokine related to ciliary neurotrophic factor (CNTF), is expressed at high levels in embryonic limb bud and is secreted by differentiated myotubes. In vitro, CT-1 kept 43% of purified E14 rat motoneurons alive for 2 weeks (EC50 = 20 pM). In vivo, CT-1 protected neonatal sciatic motoneurons against the effects of axotomy. CT-1 action on motoneurons was inhibited by phosphatidylinositol-specific phospholipase C (PIPLC), suggesting that CT-1 may act through a GPI-linked component. Since no binding of CT-1 to CNTFR alpha was detected, CT-1 may use a novel cytokine receptor alpha subunit. CT-1 may be important in normal motoneuron development and as a potential tool for slowing motoneuron degeneration in human diseases.